Genetic linkage of the Yr1 and Pm4 genes for stripe rust and powdery mildew resistances in wheat

Summary Genes Yr1 for resistance to stripe rust and Pm4a for resistance to powdery mildew showed linkage of 2.0±0.6 cM. Close repulsion linkage probably accounts for the absence in European wheats of genes Yr1 and Pm4b in combination.     

The inheritance of stem rust and leaf rust resistance in some Ethiopian wheat collections

Summary Common and durum wheat populations obtained from Sweden and originally collected in Ethiopia were screened for resistance to steum rust and leaf rust. Resistant selections of common wheat were crossed and backcrossed with either stem rust susceptible RL6071, or leaf rust susceptible Thatcher. Genetic studies, based largely on tests of backcross F₂ families, showed that four of the selections had in common a recessive gene SrA. Plants with this gene were resistant (1⁺ infection type) to all stem rust races tested. This gene was neither Sr26 nor Sr29. The resistance of other selections, based on tests with an array of rust isolates, was due to various combinations of Sr6, 8a, 9a, 9d, 9c, 11, 13, 30, and 36. One of the selections had linked genes, Lr19/Sr25. Another selection had a dominant gene for resistance (;1 infection type) to all the races of leaf rust. With the possible exception of this gene for leaf rust resistance and SrA, no obviously new resistance was found.     

Effectiveness of genes for leaf rust resistance in international wheat rust nurseries, 1970–1975

Monogenic lines resistant to leaf rust of spring and winter wheats were grown in the world wheat-producing areas from 1970 through 1975. Lines containing the alleles Lr9 (Wi), Lr9 (Tc), and Lr19 (Tc) were more resistant to the leaf rust pathogen than those containing Lr1 (Tc), –1 (Wi), –1,3 (Wi), –2A (Tc), –2A (Wi), –2D (Tc), –3 (Tc), –3 (Wi), –10 (Tc), –16 (Tc), –17 (Tc), –18 (Tc), or –2D (Pld). Monogenic line Lr1 (Wi) possibly has more than one gene for resistance and resistance properties similar to cultivars with field resistance. A computer data base was created to produce the information used in this paper.Formerly Research Agronomist, Field Crops Laboratory, now Supervisoty Computer Specialist, DSAD; and Research Plant Pathologist, Germplasm Resources Laboratory, ARS, BARC-West, Beltsville, Maryland 20705.     

Monosomic analyses of stripe rust and leaf rust resistance genes in winter wheat varieties Lüquyu and Yantar

Summary A set of 21 monosomics of Novosadska Rana-1 was used to locate the rust resistance genes of Lüqiyu, a stripe rust resistant line developed by BAU and Yantar, a leaf rust resistant wheat introduced from Bulgaria. The resistance of the former to p. striiformis race C25 was conditioned by a dominant gene located on chromosome 2B, whereas that of the latter to P. recondita race CL3 was controlled by two complementary dominant genes located on chromosomes 5A and 1D, respectively. The relationship of the stripe rust resistance gene in Lüqiyu to Yr5, Yr7 or Yr _Suwon' all located on chromosome 2B is unknown. The two complementary leaf rust resistance factors in Yantar appear to be new.     

The introduction into bread wheat of a major gene for resistance to powdery mildew from wild emmer wheat

Summary A new source of resistance to wheat powdery mildew caused by Erysiphe graminis has been transferred to hexaploid bread wheat, Triticum aestivum, from the wild tetraploid wheat, Triticum dicoccoides. The donor was crossed to bread wheat and the pentaploid progeny was then self-pollinated. Plants having a near stable hexaploid chromosome complement were selected in the F₃ progeny and topcrossing and backcrossing of these to a second wheat cultivar to improve the phenotype was undertaken. Monosomic analysis of early backcross lines showed the transferred gene to be located on chromosome 4A. The gene has been designated Pm16.     

An analysis of genes for resistance against Indian stem rust races in two bread wheat cultivars

Summary The genetic constitution of two bread wheat accessions from the International Spring Wheat Rust Nurseries (E 5883 and E 6032) has been studied for reaction to four Indian races of stem rust. Analysis of E 5883 has revealed that for each of the races 15C, 21 and 40 a single dominant gene operates for resistance. The dominant gene against race 15C was identified as Sr6. The dominant genes for resistance against races 21 and 40 were found to be different from the genes described so far. Resistance against race 122 is controlled by a single recessive gene producing characteristically a 2 type of reaction. This gene was identified as Sr8.The resistance of E 6032 against each of the races 15C, 21 and 40 is controlled by two genes, one dominant and one recessive, which act independently. Dominant genes effective against 15C, 21 and 40 were conclusively identified as Sr6, Sr5 and Sr9b, respectively. From the correlated behaviour against races 15C and 40 as well as from the phenotypes of the resistance reactions rhe same recessive gene, undescribed so far, operates against the two races. The second recessive gene operating against race 21 was also observed to be different from those so far designated. E 6032 was, however, found to be susceptible to races 122.The presence of Sr6 both in E 5883 and E 6032 against race 15C was further confirmed through F₂ and F₃ segregation data.     

Enhanced leaf rust resistance in wheat conditioned by resistance gene pairs with Lr13

Summary Leaf rust resistance gene Lr13 is present in many North American hard red spring wheat cultivars that have shown durable resistance to leaf rust. Fifteen pair-wise combinations of Lr13 and seedling leaf rust resistance genes were developed by intercrossing near isogenic Thatcher lines. In both seedling and adult plant tests, homozygous paired combinations of specific resistance genes with Lr13 had enhanced resistance relative to either parent to rust isolates that had intermediate avirulent infection types to the additional genes. In field tests, homozygous lines were more resistant than either parent if the additional leaf rust gene conditioned an effective level of resistance when present singly.     

Genes for resistance to stripe rust in four spring wheat varieties

Summary Four spring wheat (Triticum aestivum L.) varieties differing in origin and reaction in the seedling stage to pathotype CDL-6 (extant in California) were intercrossed and examined in greenhouse conditions in F₁, F₂, and F₃ generations. Digenic and transgressive segregation was found in all crosses. The four varieties each had infection types (1 immune, 9 susceptible) and putative resistance genes as follows: Anza, IT 7, YrA; Glennson 81, IT 2, Yr9; Yecora Rojo, IT 6, YrC; and Ollanta, IT 4–6, YrL. Anza was classified as susceptible, Yecora Rojo and Ollanta as intermediate in seedling resistance, and Glennson 81 as resistant in the seedling stage.     

Multiline cultivars — how their resistance influence leaf rust diseases in wheat

Summary To understand how multiline cultivars of wheat develop better protection against leaf rust, seven experimental multilines with 0, 28, 40, 50, 58, 60 and 70% susceptibility were subjected to leaf rust epiphytotics in the field along with their pure line components. A mixture comprising 12 leaf rust races, 10, 11, 12, 17, 20, 63, 77, 106, 107, 108, 162 and 162 A was used.Both the initial inoculum (Xo) and rate of increase (r) of leaf rust were substantially reduced in the multiline cultivars. Xo was reduced by 45–75% and the over-all infection rate (r) by as much as 16% over the average of components.As a result of reduced Xo and r, the intensity of leaf rust in the multilines was also significantly affected at all stages of rust development. It was reduced from 32,10 to 89.54% over the average of components differing from one multiline to another and also from time to time. The susceptible recurrent parent, Kalyansona at the peak period of rust infection exhibited 86.75% severity while in the multilines it ranged from 5.80 to 35%.The rate of increase in the multilines was found to be proportional to the logarithm of the proportion of susceptible plants in the host mixture.Further, it was found that even if as many as 50% susceptible plants are present in a multiline they would not suffer much from leaf rust damage.     

Genetics of leaf rust resistance in 13 accessions of the Watkins wheat collection

Summary The inheritance of leaf rust resistance was studied in 13 accessions of the A.E. Watkins wheat collection. Eight of the accessions (V409, V624, V628, V712, V731, V734, V745, and V855) were shown to have gene Lr33 and four of these (V409, V624, V628, and V731) also have LrW. Accessions V624 and V338 have LrB, and V377 and V488 have Lr11. V46 has an unidentified gene that gives an intermediate level of resistance. V860 has a partially dominant gene that gives a fleck reaction to avirulent isolates in the seedling stage. This gene is different from LrW and may be previously unidentified. It has been assigned the temporary gene symbol LrW2. In addition to seedling-effective genes, V46, V731, and V745 may have Lr34 and V745 may have Lr13. The adult-plant resistance in V488, V624, and V860 could not be identified. Seedling gene LrW2 and some of the adult-plant resistance should be useful sources of resistance.Contribution NO. 1576.     

The effect of transfers of alien genes for leaf rust resistance on the agronomic and quality characteristics of wheat

Summary Nine transfers of leaf rust (Puccinia recondita Rob. ex Desm.) resistance to wheat (Triticum aestivum L.) from Agropyron elongatum Host. Beauv., Triticum speltoides Tausch and rye (Secale cereale L.) were backcrossed up to 10 times to commercial wheat cultivars. The objective was to study the effect of the transfers on agronomic and quality characters and to make them available in desirable genetic backgrounds. The results varied greatly for different transfers. In four cases no promising material was obtained even after nine backcrosses. However, for the remaining five transfers material with potential as a new cultivar was obtained.     

Postulation of resistance genes to yellow rust in wild emmer wheat derivatives and advanced wheat lines from Nepal

Summary Seedlings of 38 wild emmer derivatives, and a total of 53 advanced wheat varieties/lines introduced from the International Maize and Wheat Improvement Centre (CIMMYT) or other sources, Nepalese breeding lines and local cultivars were inoculated with 18 different yellow rust isolates to postulate yellow rust resistance genes (Yr). Many wild emmer wheat derivatives used were resistant to all isolates indicating the presence of undescribed genes. Some derivatives carried Yr9, Yr6 and/or YrSU. Genes Yr1, Yr2, Yr6, Yr7, Yr8, Yr15, YrSU and YrA+ are no longer effective in Nepal; Yr4, Yr5, Yr9, Yr10, YrSP and YrSD are still effective; the effectiveness of Yr3 remains unclear. This study shows that stripe rust resistance in seedling stage of most Nepalese cultivars and advanced materials is based on Yr9 with combinations of Yr2, Yr6, Yr7, and YrA+, of which only Yr9 is still effective in Nepal. In many countries Yr9 has lost its effectiveness. Therefore the introduction of new Yr-genes from wild emmer wheat in Nepalese cultivars is highly important.     

A recessive resistance gene for yellow rust (Puccinia striiformis West.) in bread wheat (Triticum aestivum L.)

Summary Three lines derived from the old dirty Dutch land variety Gelderse Ris were resistant against race 66(70)EO(16) of yellow rust. It was found that this resistance was conditioned by one recessive gene provisionally coded yrGR.     

Monosomic analysis of stem rust resistance in the wheat cultivar Almus

Summary Monosomic analysis of resistance to stem rust, race 11 (isolate G 425) was carried out in the cultivar Almus (GDR) possessing a 1B/1R translocation. F₂ progenies of monosomic and disomic F₁ plants of Almus crossed with 21 monosomic lines of Chinese Spring were tested. Two lines (1B and 6B) differed significantly from the disomic segregation ratio by a higher number of resistant plants and two other lines (1D and 6A) by a lower number of resistant plants. The results fitted a hypothesis comprising the interaction of two genes for resistance and two inhibitors.     

Influence of wheat leaf position on leaf rust severity

Summary The relation between flag leaf position and leaf rust severity was investigated in field experiments. Different leaf angles were obtained by attaching ends of flag leaves to strings stretched at different heights along wheat rows. Leaves with angles between lamina and stem of 0° and 45° were significantly less diseased than leaves with horizontal and pendulous positions. In the experiment with seedlings, spore settling and uredia number were significantly lower on erect than on horizontal leaves. The influence of wheat leaf position changes on leaf rust severity was discussed. It has been suggested that breeding of wheat cultivars with erect leaves can improve their resistance to airborne pathogens.     

Identification and cataloguing of genetic information for resistance to wheat leaf rust

Summary Specific host-pathogen relationship is used to derive genetic information for resistance in commercial cultivars. Twenty-two cultivars were classified into 12 groups based on their reactions to 13 leaf rust (Puccinia recondita) races of India. The cultivars in each group were matched with the Lr gene carrying lines to see which genes they might possess. Confirmation of this information was sought through pedigree analyses.(1) Agra local and NP4 do not seem to have any resistance genes. (2) C306 has gene Lr14a, and NP824 one of the genes Lr12, Lr13, Lr14a or Lr22. (3) kalyansona carries Lr13 and another additional gene not in study. (4) Chhoti Lerma, NP852, Pusa Lerma, Sharbati Sonora, Shera, UP301 form one group and carry Lr1. (5) Sonalika seems to have Lr2a, Lr11 and additional genes. (6) Hy.65 has Lr10. (7) HS1076-2 and HW135 have the genes Lr2a and Lr3do. (8) HW124 carries the genes Lr1 and Lr3do. (9) Safed Lerma has Lr1 and Lr17. (10) NP846 has the genes Lr1 and Lr15. (11) HB117-107, Janak, UP215 form one group and possess the genes Lr3do and Lr15. (12) Girija possesses the genes Lr10 and Lr15.Based on such grouping of commercial cultivars for resistance genes a Catalogue system is advocated for the design of wheat breeding programmes like the development of multiline and multigene cultivars.     

Chromosome location of genes for resistance to powdery mildew in common wheat (Triticum aestivum L.) 1. Mlk and other alleles at the Pm3 locus

Summary Several wheat cultivars/lines were inoculated with isolates of Erysiphe graminis tritici to identify new genes/alleles for resistance. The wheats were tested with 13 isolates that had been characterized from responses on differential lines with known resistance genes. Gene Mlk which occurs in cultivars Kolibri, Syros, Ralle and several other European common wheats was found to be an allele at the Pm3 locus and is now designated Pm3d. The mildew resistance in an old Australian wheat, W150, is conferred by a single gene also allelic to Pm3 and now designated Pm3e. The near-isogenic line Michigan Amber/8^*Cc possesses another allele now designated Pm3f. A Syrian land variety of common wheat shows mildew resistance that is conditioned by the combination of genes Pm1 and Pm3a. Finally, two accessions of Triticum aestivum ssp. sphaerococcum appeared to possess the Pm3c allele.     

Transgressive segregation for resistance to yellow rust in wheat

Summary Crosses were made between wheat varieties Joss Cambier, Nord Desprez and Maris Bilbo, all classified as susceptible to yellow rust in field tests, and between Cappelle Desprez and Maris Huntsman, both classified as moderately and durably resistant. Selection for resistance to yellow rust among the progeny was carried out using races of Puccinia striiformis able to overcome all the known race-specific components of resistance in both parents of each cross. Lines with greater resistance than in both parents were obtained from each cross, those with greatest resistance being obtained from the cross between the moderately resistant parents. Three lines selected for resistance from the cross of Joss Cambier with Nord Desprez and one from the cross of Cappelle Desprez with Maris Huntsman, together with the parents, were tested in the field with 12 races of P. striiformis. Nord Desprez possessed a previously undetected race-specific component. The selected lines also displayed race-specific resistance, some of which was clearly related to race-specificity of the parents, and a component of resistance, greater than in both parents, that was effective against all 12 races. The possible origin and potential durability of this transgressive level of resistance is discussed. It is suggested that such transgressive resistance is more likely to be durable if it is derived from parents that have shown durable resistance.     

Variation of characters in near-isogenic lines of wheat with added genes for leaf rust resistance

Summary Using the cultivar Arina as the recurrent parent, six backcrosses were made with two donor lines carrying the leaf rust resistance genes Lr1 and Lr9, respectively. Selection for leaf rust resistance occurred at the seedling stage in the greenhouse; the first plants transferred to the field were BC₆F₄s. Frequency distribution of the 332 Lr1/7 × Arina and the 335 Lr9/7 × Arina lines showed continuous variation for yellow rust resistance and heading date in these leaf rust near-isogenic lines (NILs). Similar results were also obtained for plant height, for resistance to powdery mildew and glume blotch, as well as for baking quality characters in another set of more advanced NILs. The available information on the behaviour of one of the parents of cultivar Arina led to the conclusion that the expressed yellow rust resistance is quantitative and might possibly be durable.     

Molecular mapping of powdery mildew resistance genes in wheat: A review

Powdery mildew, caused by Blumeria graminis f. sp. tritici (syn. Erysiphe graminis f. sp. tritici), is one of the most important diseases of common wheat (Triticum aestivum L.) worldwide. Molecular mapping and cloning of genes for resistance to powdery mildew in hexaploid wheat will facilitate the study of molecular mechanisms underlying resistance to powdery mildew diseases and help understand the structure and function of powdery mildew resistance genes, and permit marker-assisted selection in breeding programs. So far, 48 genes/alleles for resistance to powdery mildew at 32 loci have been identified and located on 16 different chromosomes, of which 21 resistance genes/alleles have been tagged by restriction fragment length polymorphisms (RFLPs), random-amplified polymorphic DNAs (RAPDs), amplified fragment length polymorphisms (AFLPs), sequence characterized amplified regions (SCARs), sequence-tagged sites (STS) or simple sequence repeats (SSRs). Several quantitative trait loci (QTLs) for adult plant resistance (APR) to powdery mildew have been associated with molecular markers. The detailed information on chromosomal location and molecular mapping of these genes has been reviewed. Isolation of powdery mildew resistance genes and development of valid molecular markers for pyramiding resistance genes in breeding programs is also discussed.